Oakes Irrigation Research Site
Carrington Research Extension Center * North Dakota State University
P.O. Box 531, Oakes, ND 58474-0531, Voice: (701) 742-2189, FAX: (701) 742-2700, email: rgreenla@ndsuext.nodak.edu

CARROT WEED CONTROL STUDY, 2001

Richard Greenland

Table 39. Weed control and crop injury ratings

Table 40. Number of roots and yield of carrots

Table 41. Carrot root characteristics

Only a few herbicides are available for weed control in carrots. Treflan, Lorox, Poast and Fusilade are the most commonly used. In this study we evaluated five additional herbicides, Authority, Outlook, Dual II Magnum, Dacthal, and Valor, for their usefulness in carrot production.

MATERIALS AND METHODS

Soil:	Embden Sandy Loam and Maddock Sandy Loam; pH=7.2; 2.5% organic matter; soil-P and soil-K were very high; soil-S was very low.
Previous crop:	2000 - cabbage; 1999 - onion; 1998 - pepper.
Seedbed Preparation:	Chisel plow twice April 29. Multiweeded (field cultivated) three times; once May 9 to incorporate fertilizer and twice May 14 to incorporate herbicide.
Planting:	Direct seeded Bolero carrots on May 16 with a Monosem precision vacuum planter set to plant a row of barley cover crop between the carrot rows. Carrot planting pattern was 3 lines per row (2 inches between lines in the row) on 18-inch centers. Planting rate was about 800,000 seeds/acre.
Plots:	Plots were 17 ft long by 6 ft wide with a 2-ft check strip between plots. There were 4 reps.
Fertilizer:	On April 19, broadcast 10 lbs N/acre and 50 lbs P₂O₅/acre as 10-50-0 and 18 lbs N/acre and 20 lbs S/acre as 21-0-0-24. Sprayed 50 lbs N/acre as 28-0-0 on May 9. Fertigated 35 lbs N/acre as 28-0-0 on July 2.
Irrigation:	Overhead sprinkler irrigation as needed.
Pest control:	Treflan (1.5 pt/acre on May 14) and Poast + Dash (1.5 pt + 1 pt/acre on June 12) were applied to all plots. All plots were hand weeded July 5 and 6. See Table 38 for other weed control treatments. We sprayed Sevin (1 qt/acre on July 12, July 30, and Aug 27) and Asana (8 oz/acre on July 20, Aug 8, and Aug 15) to control leafhopper.
Harvest:	Carrots were harvested on September 4. The harvest area was 3 ft of the center two rows of each plot.

RESULTS

A single application of Lorox was not enough to control hairy nightshade. A second application of Lorox controlled nightshade completely without injury to the carrots. In previous years we found that Dual or Outlook (Frontier) applied before carrots emerged injured carrots. This year we found that if applied after carrots emerge they didn’t control hairy nightshade. Authority controlled hairy nightshade but injured carrots when applied when carrots were 1.5 or 3 inches tall. Valor applied PRE reduced carrot stand, which caused an increase in carrot size and number of carrots with multiple roots and a decrease in carrot quality and yield. Valor applied POST burned the carrot leaves, killing some carrots, but most plants survived and revived, and carrot stand and yield were slightly reduced. Dacthal controlled nightshade without injuring carrots. Dacthal appears promising for weed control in carrots along with Lorox and Treflan.

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Table 38. Treatments for the Oakes Irrigation Research Site 2001 carrot weed control study.

Treatment number	Chemicals	Rates (product/acre)	Application Timing¹
1	Valor	1.5 oz	PRE
2	Lorox	1 lb	PRE
3	Lorox + Authority	1 lb + 3 oz	PRE + POST
4	Lorox + Dual II	1 lb + 1 pt	PRE + POST
5	Lorox + Outlook	1 lb + 1 pt	PRE + POST
6	Lorox + Valor	1 lb + 1.5 oz	PRE + POST
7	Lorox + Lorox	1 lb + 1.5 lb	PRE + LPOST
8	Lorox + Authority	1 lb + 3 oz	PRE + LPOST
9	Valor + Lorox	1.5 oz + 1.5 lb	PRE + LPOST
10	Dacthal + Lorox	8 lbs + 1.5 lb	EPOST + LPOST

¹PRE was just after planting (May 16). EPOST was on May 29, barley was 3 to 4" tall, carrot was ½” tall, and weeds were about ½” tall. POST was on June 12 when carrots were 1.5" tall and weeds were mostly less than 1" tall. LPOST was on June 21 when carrots were 3" tall and weeds (mostly hairy nightshade) were 1 to 5" tall.

All treatments include Treflan applied PPI on May 14 and Poast + Dash applied POST on June 12.

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Table 39. Weed control and crop injury for the Oakes Irrigation Research Site 2001 carrot weed control study.

Trt¹ No.	June 20 ratings²			July 4 readings²				July 5 & 6 weed time³
Trt¹ No.	stand	crop injury	hairy nightshade	crop height	stand	crop injury	hairy nightshade	July 5 & 6 weed time³
	------------- 0 to 10 -------------			inches	------------- 0 to 10 -------------			minutes

1	5.8 c⁴	2.3 bc	10.0 a	7.8 bc	5.5 c	0.0 a	10.0 a	5.3 a
2	8.8 a	0.0 a	7.3 bc	10.0 a	8.8 a	0.0 a	6.5 b	21.3 c
3	8.0 ab	5.5 d	10.0 a	7.0 c	6.3 c	1.8 b	10.0 a	5.8 a
4	8.8 a	0.5 a	8.0 b	9.8 a	8.5 a	0.0 a	7.5 b	14.5 b
5	8.5 ab	3.0 c	7.8 b	6.3 c	7.5 b	3.5 c	8.0 b	13.5 b
6	7.5 b	5.5 d	10.0 a	6.8 c	6.3 c	0.5 a	10.0 a	1.3 a
7	8.8 a	0.0 a	7.3 bc	9.5 a	8.3 ab	0.0 a	10.0 a	4.3 a
8	8.8 a	0.0 a	6.5 c	8.8 ab	7.5 b	2.0 b	10.0 a	4.0 a
9	5.8 c	1.5 b	10.0 a	7.8 bc	6.0 c	0.0 a	10.0 a	3.3 a
10	8.8 a	0.0 a	9.5 a	9.5 a	8.5 a	0.0 a	10.0 a	2.5 a

Prob.	<.0001	<.0001	<.0001	<.0001	<.0001	0.0001	0.0002	<.0001
C.V.	9	34	8	9	71	13	12	60

¹See Table 38 for treatments.

²Ratings are from 0 to 10: 0 = no weed control or crop injury, 10 = complete weed control or all carrots dead. Crop injury on July 4 does not include stunting which is given in the column “crop height”.

³On July 5 and 6 the plots were weeded. Values given in this column are the average time to weed one 6 by 17 ft plot.

⁴Values in the same column followed by the same letter are not significantly different at the 0.05 level.

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Table 40. Number of roots and yield of carrots in the Oakes Irrigation Research Site 2001 carrot weed control study.

Trt.¹ No.	Number of carrot roots (by carrot diameter)				Carrot yield (by carrot diameter)
Trt.¹ No.	>1.5"	1 to 1.5"	US #1	total	>1.5"	1 to 1.5"	US #1	total
	------------------- 1000s/acre -------------------				--------------------- tons/acre --------------------

1	69.0	20.6 e²	92.0 d	133.1 e	15.3 a	2.2 d	17.7 c	27.7 abc
2	83.5	151.3 bc	274.7 ab	331.5 ab	12.9 abc	12.0 abc	26.2 ab	32.2 a
3	53.2	111.3 d	209.3 c	258.9 cd	10.0 bcd	9.1 c	20.3 bc	23.0 c
4	66.6	176.7 ab	300.1 ab	344.9 ab	10.3 bcd	14.8 a	26.7 a	31.3 a
5	54.5	146.4 bcd	243.2 bc	298.9 bcd	8.2 d	12.0 abc	21.4 abc	25.2 bc
6	82.3	119.8 cd	211.8 c	242.0 d	14.2 ab	10.4 bc	24.8 ab	28.4 abc
7	69.0	167.0 ab	271.0 ab	311.0 bc	10.7 bcd	14.1 a	25.9 ab	31.1 ab
8	67.8	167.0 ab	286.8 ab	338.8 ab	9.7 cd	13.2 ab	24.4 ab	28.6 abc
9	64.1	14.5 e	78.7 d	118.6 e	14.0 abc	1.3 d	15.2 c	24.9 c
10	71.4	196.0 a	324.3 a	378.7 a	10.9 bcd	13.8 ab	26.3 ab	31.3 a

Prob.	0.33	<.0001	<.0001	<.0001	0.048	<.0001	0.006	0.04
C.V.	26	21	17	15	27	24	19	14

¹See Table 38 for treatments.

²Values in the same column followed by the same letter are not significantly different at the 0.05

level. If no letters follow values in a column then there were no significant differences between

values in that column.

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Table 41. Carrot root characteristics for the Oakes Irrigation Research Site 2001 carrot weed control study.

Treatment number	Average root length	Average root size	Multiple root yield	% US #1 yield	Overall score
	inches	oz/root	tons/acre	%	1 to 10

1	7.3 ab²	6.4 a	8.7 a	63.5 b	3.5 b
2	6.6 cd	3.1 bc	4.2 b	81.3 a	5.9 a
3	6.7 cd	3.1 bc	2.3 b	87.7 a	6.0 a
4	6.6 cd	2.8 c	3.5 b	84.5 a	5.8 a
5	6.7 cd	2.8 c	2.6 b	84.9 a	6.1 a
6	7.0 bc	3.8 b	3.0 b	87.2 a	7.3 a
7	6.7 cd	3.1 bc	3.9 b	83.6 a	7.0 a
8	6.4 d	2.7 c	3.2 b	85.1 a	6.3 a
9	7.6 a	6.4 a	8.6 a	62.1 b	3.3 b
10	6.8 bcd	2.6 c	3.9 b	83.5 a	6.0 a

Probability	0.009	<.0001	0.008	0.003	0.01
C.V. (%)	6	13	58	12	26

¹See Table 38 for treatments.

²Values in the same column followed by the same letter are not significantly different at the 0.05 level.